1. Field of the Invention
The present invention is directed to an improvement of an index device wherein a multiplicity of cards having telephone numbers and other index items recorded are accomodated in between a receptacle and a cover member, and a sheet of the card on a desired page appears when opening the cover member.
2. Description of the Prior Art
The index device is provided with a good number of cards for keeping records of telephone numbers and other indexing items, these cards being accomodated in between the receptacle and the cover member. This kind of index device is arranged in such a way that the card on the desired page is retrieved by means of a slider, the cover member is unlocked from the receptacle by pushing a knob with a finger and is soon opened by dint of spring forces, and the card (upper portion) just before the one on the desired page is raised up together with the cover member. Therefore, if the desired page is positioned beneath a multiplicity of cards, the cover member is situated so as to be integral with a great majority of such cards.
In order to open the card just before the desired page together with the cover member even if the desired page among a good number of cards is in any position, it is required to invest a spring with large resilient repulsion forces sufficient to open the cover member from the receptacle. Videlicet, if the spring lacks resilient repulsion forces, the card on the desired page is by no means opened because of a lack of the forces when the desired page is situated under a good number of the cards. While on the other hand, if the spring is strengthend very much, the spring is so intensive that the cover member is instantaneously opened at a high velocity when the desired page is positioned on a multiplicity of the cards. As a result, the indexing device as a whole vibrates on the desk, which is conclucive to a problem of making a noisy sound.
To cope with this problem, the receptacle of the indexing device is composed of a thick iron plate or is provided with a suitable heavy weight to offset the reaction when the cover member is quickly opened. This arrangement, however, brings about disadvantages of being costly both in material and in transport. Besides, it makes no contribution to the fundamental solution of restraining the cover member from being quickly opened. This quick opening action of the cover member unfavourably induces not only the vibration but also adsorption of the card on the opening page to the next card. These problems are not obviated by the aforementioned arrangement. The present applicant who had been inspired by the above-described circumstances developed an indexing device which makes the most of viscosity intended to resist the opening forces of the cover member. This proposal is disclosed in the specification of Japanese Patent Utility Model Laid-Open No. 171377/1985.
The already disclosed indexing device is, as illustrated in FIG. 5, arranged as follows. A bearing member consisting of annular grooves 42 formed in the a cover member 41 and protrusions 43 which are formed on a receptacle 40 and are rotatably fitted in the annular grooves 42 is provided at a portion where the receptacle 40 and the cover member 41 are axially attached. The annular grooves are filled with a viscous substance made of resin or the like which serves to yield stopping forces against the opening motion of the cover member in order to moderate the intensive repulsion when the cover member is unfolded in a gradually accelerated manner by dint of a given reverse spring immediately after releasing the hook thereof, whereby the cover member is opened at a substantially equalised velocity.
All the above-mentioned problems could be solved by the thus constructed indexing device which is advantageous in terms of function and production costs as well. The annular protrusions are fitted in the annular grooves, and gaps formed therebetween are charged with the viscous substance like silicon grease. Such a constitution, however, causes a problem in which the viscous substance leaks out little by little during a long period of use and the leakage spoils the function thereof.
The viscous substance supplied to the bearing member is intruded in the narrow gaps formed between the inner walls of the annular grooves and the protrusions, its quantity therefore becomes extremely small. In proportion as the amount of the viscous substance increases, the capability to correct the unevenness in velocity of inversion of the spring which is generated with the passage of time is enhanced. Hence, it is highly desirable that the limited space be filled with the greatest amount of viscous substance.